1. Field of the Invention.
This invention relates to method and apparatus for injecting samples of material into a high pressure environment. More particularly, the invention pertains to sample injection apparatus for use in liquid chromatography.
2. Description of the Prior Art.
Liquid chromatography pertains to a particular variety of equipment and techniques for analyzing the components of an unknown sample of liquid material, qualitatively and/or quantitatively. According to chromatographic techniques, a column is provided which is packed with a finely divided material. The packing material provided is chosen in accordance with its affinity for attracting certain elements to adsorb or cling to it. The sample is forced in a stream of carrier liquid through the column, and each of the components passes through the column in a time pattern which is a function of the degree of tendency of that particular component to be adsorbed by the packing material. By detecting variations in properties of the liquid emerging from the column, and plotting these variations against time, certain information can be derived as to the nature and amount of the components of the unknown sample. For example, the presence of a given component of the sample may be known to effect a change in a particular property of the liquid emerging from the column such that a maximum value of that property will occur at a predetermined time after the sample is introduced into the column. By observing where such peaks occur, the nature of various components of the sample may be determined with a significant degree of certitude and repeatability.
It has been found that if the sample is driven through the column in a carrier stream at very high pressure, a consequent reduction in the time for analysis of each sample is observed, due to the more rapid passage of the sample through the column. Such high pressure techniques have certain disadvantages, however.
There is difficulty and great expense in procuring and manufacturing seals which are sufficient to handle the extreme pressure drops which often occur between the sample injectors and the stream into which the sample is to be forced. Often, these pressure drops result in leakage and consequent inaccuracy of analysis.
In the past some effort has been made to obviate this problem by stopping the flow of carrier liquid in the high pressure line to the column during injection. This is time consuming and requires frequent starting and stopping of the high pressure pumps for driving liquid through the column, which increases wear on such components and their control elements.
Even when high pressure injection has been possible, it often results in a momentary drop in the carrier line pressure which adversely affects resolution of the system.
It is therefore an object of this invention to provide a method and apparatus for introducing a sample of material into a very high pressure line of flowing carrier liquid, without interrupting the flow of liquid in the line or reducing the line pressure.